1. Technical Field of the Invention
The invention relates to a process for the preparation, preferably from waste materials, of silicate foam having with closed pores and the product produced by the process.
By the process according to the present invention silicate foam granules are produced, which can be used alone or together with inorganic or organic binding material for manufacturing of sheets or articles of desired shape.
The product according to the invention is of low specific weight, flame-proof and has excellent thermal insulating, sound-proofing and anti-vibration properties.
2. Description of the Related Art
Several processes are known for the preparation, of glass foams.
In the Hungarian patent No. 171 046 is disclosed a process for the manufacture of foamy product from ground waste glass. According to said process the waste glass is mixed with powdered alkali metal hydroxides, phosphoric acid and/or silicone fluoride as melting point lowering additives, and the foaming is carried out in the presence of a gas-forming material at a temperature of 600-850xc2x0 C.
According to the process disclosed in the U.S. Pat. No. 4,413,907 glass powder, additives and water are mixed, then in a furnace at high temperature foamy product is manufactured.
The U.S. Pat. No. 4,734,322 relates to a process characterised by adding a mixture of calcium carbonate and magnesium carbonate to glass powder, then from the mixture obtained foamy product is manufactured at a temperature of 700-800xc2x0 C.
The Japanese patent publication No. 03 13 7038 concerns a process for the production of glass foam; according to said process the starting glass powder is mixed with 1-5% by weight of strontium carbonate and from this mixture thermal insulating glass foam is produced.
The disadvantage of the processes mentioned above is that only a small part of the glass foam granules produced by them have closed pores, and therefor their strength properties are not satisfactory, they can not be used as anti-vibration materials.
Our aim was to work out a process by which the disadvantages of the above mentioned processes can be eliminated and silicate foam product can be manufactured with closed pore structure and high strength.
As suitable starting material waste glass powder, ground enamel frit, waste moulding sand, waste ceramic, silicate waste from the manufacture of electric bulb or fluorescent lamp or other organic or inorganic silicate waste are used, but original glass powder or ground silicate can also be applied.
Accordingly, the present invention relates to a process for the preparation, preferably from waste materials, of silicate foam having closed pores by mixing silicate powder, gas-forming material, alkaline solution, optionally wetting the mixture with water, then homogenising, granulating and subjecting to heat treatment the mixture obtained.
The process characterised in that to 100 parts by weight of silicate powder, preferably waste glass powder, waste enamel frit, waste moulding sand, waste ceramic, organic or inorganic silicate waste or a mixture thereof having a specific surface of 2000-8000 cm2/g 1-10 parts by weight of gas forming material of particle size 10-100 xcexcm, preferably ground limestone and/or dolomite and/or magnesite and/or witherite is added, the mixture is homogenised and then 0.5-15 parts by weight of montmorillonite optionally activated with a 1-10% by weight solution of alkali metal hydroxide or metal carbonate, and/or serpentine and/or alumina and/or aluminium oxide hydroxide, optionally 0.2-3 parts by weight of alkali metal hydroxide or metal carbonate in form of 1-10% by weight solution, further 0.5-2 parts by weight of alkali hydrogen phosphate or alkali dihydrogen phosphate or a mixture of alkali metal phosphate and sodium silicate in form of aqueous solution, as well as 0.01-5 parts by weight of a rare earth metal oxide or a mixture of such oxides, optionally 0.1-5 parts by weight of a coloured metal oxide or a mixture of such oxides or a heavy metal oxide or a mixture of such oxides are added, then the mixture obtained this way is homogenised, if desired wetted with water and granulated, then pre-dried, the granules are coated with 1-5 parts by weight of titanium dioxide and/or titanium oxide hydroxide and/or aluminium oxide hydroxide, then subjected to heat treatment at a temperature of 720-1000xc2x0 C., optionally the granules obtained are coated with 0.1-1% by weight of polymer film or optionally 90-50 parts by weight of granules are mixed with 10-50 parts by weight of organic or inorganic binding material and shaped to the desired form.
A further object of the invention is a granulated silicate foam manufactured by the above process and having 0.4-0.45 g/cm3 bulk weight and closed pores, which optionally contains 0.1-2% by weight of polymer film on the surface or a shaped article containing 90-50 parts by weight of silicate foam granules having closed pores and manufactured by the above process and 10-50 parts by weight of organic or inorganic binding material.
The shaped article can be a sheet or a building block of desired shape.
The role of the rare earth metal oxide or the mixture of such oxides used in the process according to the invention is to adjust the optimal surface tension of the mixture and to induce a quick crystallisation process in the material. This way the strength of the granules formed is surprisingly increased.
The addition of titanium dioxide or titanium oxide hydroxide before the beat treatment prevents the adhesion of the granules.
By using coloured metal oxide or a mixture of such oxides as well as heavy metal oxide or a mixture of such oxides in the process according to the invention, granules of desired colour can be produced.
The witherite optionally used in the process is a mineral based on barium carbonate.
In the process as alkali solution the aqueous extract of the ash of sunflower seed shell can also be used.
The activation of montmorillonite and/or serpentine-like minerals can be carried out either before mixing or in situ, when mixing it/them with the silicate powder.
If desired the surface of the granules can be coated by thermoplastic or thermosetting polymer film. When the granules are mixed with binding material, shaped articles can be manufactured from the mixture.
As binding material cement, gypsum, bitumen, thermoplastic polymers or thermosetting synthetic resins can be applied.
The process and the product according to the invention have the following advantages:
The process provides the production of silicate foam granules which have closed pores, more homogenous particle size than that produced by the known processes, and improved strength properties.
By the process not only waste glass but other waste silicate can be worked up to a product with thermal insulating and soundproofing properties.
The product obtained by this process is an excellent anti-vibration material.
By the process according to the invention not only waste materials but original glass powders and silicate powders can be worked up to silicate foam with closed pores.
The process according to the invention is illustrated by the following examples.